The present invention relates to a heat-sensitive lithographic printing plate, particularly a heat-sensitive lithographic printing plate wherein images are formed by the action of heat, and further to a substrate used therein and a method of producing such a substrate. More specifically, the present invention relates to a heat-sensitive lithographic printing plate capable of forming images by low-energy or short-duration laser irradiation, and further to a substrate used therein.
In a heat-sensitive lithographic printing plate of the type which contains in its heat-sensitive layer a light-to-heat converting material capable of absorbing near infrared laser beams and converting the absorbed beams into heat, images for printing are formed through a process that the heat-sensitive layer gets heated in areas irradiated with near infrared beams, thereby causing an increase in solubility to alkali or heat curing in the foregoing areas to form images, and the non-image areas are dissolved and removed by development-processing.
As to the sensitivity in such a system, a matter of concern is not how much energy (i.e., much absolute value) is applied in gross by laser-beam irradiation, but the problems are how to convert the light energy into heat at great efficiency and how to efficiently raise a temperature of the heat-sensitive layer by the converted heat.
The former problem has been studied diversely from the viewpoints of newly developing light-to-heat converting materials, providing a reflection layer and devising layer structures to attain the purpose.
The latter problem has been supposed to be caused mainly by diffusion of heat generated in the heat-sensitive layer into a metallic support, and so it has been examined from the viewpoint of inhibition of thermal diffusion. As a result, the heat-insulating layers and the supports made of heat-insulating materials as described below are disclosed.
For instance, JP-A-11-65105 (the term xe2x80x9cJP-Axe2x80x9d as used herein means an xe2x80x9cunexamined published Japanese patent applicationxe2x80x9d) proposes to provide a heat-insulating layer containing a polyvinyiphosphonic acid in an amount of 0.001 to 10 mg/m2 on an anodically oxidized film. For actually producing the intended effected by the formation of a heat-insulating layer, however, the heat-insulating layer is required to have a certain thickness or above. As a result, the heat-insulating layer presents a problem of adhesion to a heat-sensitive layer or a support and causes film-residue trouble. support and causes a film-remaining trouble.
JP-A-10-39496 specifies the thermal conductivity of a support, and proposes a method of using polyethylene terephthalate having a low conductivity or foamed polyethylene terephthalate still lower in conductivity. And the heat-sensitive lithographic printing plates utilizing polyethylene terephthalate as support are already on the market.
In addition, the composite support formed by bonding a polyethylene terephthalate film as heat-insulating layer to an aluminum support has been proposed, and it is commercially available. In the case of using such an organic material, however, there occurs a problem that traditional arts for an aluminum support-used PS plate, inclusive of the art of close adhesion, the art of rendering the support surface hydrophilic and the art of improving printing quality through the surface water control, cannot be applied to the composite support as described above.
As mentioned above, many techniques for preventing thermal diffusion into a metallic support, such as the prevention by providing a heat-insulating layer or making a support from a heat-insulating material, have been proposed. With the current state of the arts, however, the market""s demands for diminution of laser energy required for image formation and reduction in writing time are not sufficiently satisfied yet.
On the other hand, no arts based on the viewpoint of inhibiting the thermal diffusion in a heat-sensitive layer (image-forming layer) are disclosed yet.
Therefore, an object of the present invention is to solve the aforementioned various pending problems. More specifically, one object of the present invention is to provide a heat-sensitive lithographic printing plate wherein the diffusion of heat into its aluminum support is inhibited to enable image formation by irradiation with laser at a lower energy level.
Other objects of the present invention are to provide a substrate for lithographic printing plate, which can inhibit the heat diffusion into an aluminum support, has water receptivity equivalent to those of anodically oxidized supports hitherto used for printing plates and can ensure image formation by laser irradiation at a lower energy level, and to provide a method of producing such a substrate.
As a result of our intensive study on methods of inhibiting the diffusion of heat inside the image-forming layer while making use of the techniques for supports having water-receptive surfaces, it has been found that the diffusion of heat can be inhibited and images can be formed with a low-energy laser irradiation when polymer hollow microspheres, each of which is walled with a highly cross-linked polymer film and has a void on the inside, are added to a heat-sensitive layer (or an image-forming layer) or an undercoat layer provided on a support, thereby achieving the present invention.
Further, it has been found that when the substrate used for a lithographic printing plate comprises an aluminum support, a layer of hollow microspheres and an aluminum hydrate or oxide layer, which are arranged in order of description, the heat diffusion can be inhibited, images can be formed by irradiation with low-energy laser, and besides, the water-receptive surface similar to usual ones can be obtained, thereby completing the present invention.
More specifically, the following are primary embodiments and preferred embodiments of the present invention:
(1) A heat-sensitive lithographic printing plate comprising a support having thereon an undercoat layer and a heat-sensitive layer in this order, at least one of said undercoat layer and said heat-sensitive layer comprising polymer hollow microspheres having voids on the inside.
(2) A heat-sensitive lithographic printing plate comprising a support having thereon a heat-sensitive layer, said heat-sensitive layer comprising polymer hollow microspheres having voids on the inside.
(3) The heat-sensitive lithographic printing plate as described in Embodiment (1), wherein the support is an aluminum sheet or an aluminum alloy sheet and the undercoat layer is covered with a filmy layer of aluminum hydrate and/or aluminum oxide.
(4) The heat-sensitive lithographic printing plate as described in Embodiment (3), wherein the filmy layer of aluminum hydrate is formed by a hydration treatment, and the filmy layer of aluminum oxide is formed by subjecting the filmy layer of aluminum hydrate to a anodic oxidation treatment.
(5) A substrate for a lithographic printing plate comprising an aluminum or aluminum alloy sheet support, further having on the support an undercoat layer comprising hollow microspheres and a filmy layer of aluminum hydrate and/or aluminum oxide in this order.
(6) A method of producing a substrate for a lithographic printing plate, comprising steps of:
providing an undercoat layer comprising hollow microspheres on an aluminum or aluminum alloy sheet support, and
forming a filmy layer of aluminum hydrate by subjecting the undercoat layer to hydrate treatment.
(7) A method of producing a substrate for a lithographic printing plate, comprising steps of:
providing an undercoat layer comprising hollow microspheres on an aluminum or aluminum alloy sheet support,
forming a filmy layer of aluminum hydrate by subjecting the undercoat layer to hydrate treatment, and
forming on the filmy layer of aluminum hydrate an oxide film layer as the topmost layer by subjecting the filmy layer to anodic oxidation treatment.
As to the addition of a granular substance to a layer which is formed on a support as a constituent of a heat-sensitive lithographic printing plate, the following techniques have been proposed.
For instance, the method of incorporating particles having an average diameter of 50 xcexcm or less into a UV absorbent-added layer provided on a light-sensitive layer constituting a lithographic printing plate is disclosed in JP-A-7-311458.
JP-A-9-29924 discloses the method of improving image strength by adding a granular substance to an image-receiving layer provided underneath an image-forming layer capable of fusing by heating via exposure so that voids measuring 0.01 to 10 xcexcm in size are formed and making the image-receiving layer go into the voids under fusing.
JP-A-11-48630 discloses the technique of improving stain resistance and abrasion resistance in non-image areas by using hydrophilic binder and granular inorganic filler in combination to form a non-image area layer having a porous structure specified by a voidage of 30 to 80% and an average void diameter of 0.05 to 1 xcexcm.
Most of the granular substances added in the present inventions described above are inorganic particles, and they are not intended for inhibition of thermal diffusion.
On the other hand, JP-A-11-268439 and JP-A-11-309953 disclose the image layers to which particles are added. In these cases, the particles are defined as water-insoluble particles including organic particles, but the gist of such techniques is considered to consist in formation of a porous structure by making use of gaps among particles.
In the case of adopting the above-described means of providing layers of fine particles, the fine particles are fixed in the layers with the aid of binders. However, it is very difficult to make those layers have water receptivities on the same level as those of well-known anodically oxidized films.
A striking feature of polymer particles used in the heat-sensitive lithographic printing plates of the present invention consists in that the polymer particles are hollow particles (including hollow microspheres) and enclose therein a gas phase (air) which can promise greater heat-insulating effect than an organic material forming their respective envelopes.
In a heat-sensitive lithographic printing plate of the present invention, the undercoat layer or the heat-sensitive layer provided on a support contains polymer hollow microspheres, which each have a void on the inside and are enclosed with a highly cross-linked polymer. By the incorporation of such particles, the diffusion of heat can be inhibited and the heat generated through light-to-heat conversion can be utilized efficiently for the image formation. Accordingly, a saving in laser energy required for image formation can be achieved and the writing time can be shortened. As a result, it becomes possible to use cheap laser devices of low power, and so the cost of a plate-making system can be reduced.
In accordance with the substrate used for a lithographic printing plate and the method for production thereof, of the present invention, a layer comprising hollow microspheres (sometimes, referred to as an undercoat layer) is provided on a support, and further thereon a layer of aluminum hydrate or oxide is provided. By these layers arranged on a support, the diffusion of heat can be inhibited, and the heat generated through light-to-heat conversion can be utilized efficiently for the image formation. Thus, a saving in laser energy required for image formation can be effected and the writing time can be shortened. As a result, it becomes possible to use cheap laser devices of low power, and so the cost of a plate-making system can be reduced.
A cross-section view showing an example of a layer structure of a substrate of the present invention and a heat-sensitive lithographic printing plate using such a substrate is exhibited hereinafter as FIG. 4. Therein, the substrate 15 for a lithographic printing plate of the present invention has an undercoat layer containing hollow microspheres 12 on the surface of an aluminum support 11, and further has on the undercoat layer an aluminum hydrate or oxide layer 13 so as to cover the hollow microspheres 12.
And the layer on the substrate 15 is an image-forming layer (heat-sensitive layer) 14 formed on the substrate 15.